1. Field of the Invention
The present invention relates to a visual acuity testing apparatus which presents a test optotype to an eye to be examined for testing or measuring visual acuity or the like. More particularly,. the present invention relates to a night visual acuity (night vision) testing apparatus used for a driving aptitude test or the like.
2. Description of Related Art
Conventionally known as a visual acuity testing apparatus is an apparatus which presents test optotypes disposed inside a casing through binocular test windows for testing or measuring visual function such as visual acuity and the like. As this kind of apparatus, there is an apparatus whose optotype presentation optical system is disposed inside a casing in a manner that a test distance of the optotype is optically long distance (for example five meters). The visual acuity test is measured through examining how well an examinee sees the optotypes. Additionally, among this kind of apparatus, there is a night visual acuity testing apparatus which is used for the driving aptitude test or the like. In a night visual acuity testing apparatus, first, the eye is shown space inside the casing that has been adjusted to be as bright as the daytime through the test windows in order to cause light adaptation in the eyes. After this, the optotypes are presented under dark conditions in the space inside the casing, then the visual acuity recovering time is taken until the eye visually identifies the optotypes, which is measured.
However, in a conventional visual acuity testing apparatus, there is a problem such that the shapes of the optotypes are visible because incident light from the test windows enters inside the casing and reflects from surfaces of the optotypes. This causes a problem that a test with high accuracy is hard to be achieved. The problem is much more serious in the night visual acuity testing apparatus. For prevention, conventionally, when the test is carried out in a bright room, for example, the examinee""s head is covered with a blackout curtain, which is inconvenient.
Conventional visual acuity testing apparatus adopts a way in which an examinee looks into one casing with the both eyes through the binocular test windows. In case that the both eyes individually look into the casing, the eyes feel uncomfortable upon observing the optotype owing to different distances from a right interior wall and from a left interior wall. Under such observation, it is difficult to produce the conditions that the examinee sees five meters ahead so that accuracy of the test decreases compared with a visual acuity test carried out in real conditions that the examinee sees five meters ahead.
Furthermore, conventional night visual acuity testing apparatus has following problems. In the night visual acuity test, after light adaptation, if the examinee can judge presented optotypes in a visual field (the casing) in the same low brightness, he makes responses with a response switch. The apparatus carries out measurement of the time from start of presenting the optotypes. At a point of inputting results with the response switch, the apparatus stops time measurement. In case that judgement results of the optotypes by the examinee is right, the lapsed time to a point of time when the response is inputted, is determined as the visual acuity recovering time. Additionally, in case that no response is made after 60 seconds from start of measuring the visual acuity recovering time (start of presenting the optotypes), the test is terminated leading the lowest evaluation value as the result. However, if just one response leads the test result as mentioned above, in case that judgement results of optotypes are in error, it is necessary to carry out the test again from the start, which takes time to obtain test results. There is a problem concerning test accuracy considering possibility that a response as the result of a guess happened to be a right response. In the test for the elderly, in many cases, they can not respond after 60 seconds have passed from starting of measurement, thus, the visual acuity recovering time is difficult to be evaluated.
The present invention has been made in view of the above circumstances and has an object to overcome the above problem and to provide a visual acuity testing apparatus which achieves tests with high accuracy even in a bright room. Additionally, it is also an object of the present invention to provide a visual acuity testing apparatus which produces far-vision without causing uncomfortablness in order to carry out tests with high accuracy.
Further, another object of the present invention is to provide a night visual acuity testing apparatus which can obtain test results with high efficiency and high accuracy, and further more to provide a visual acuity testing apparatus which gives useful test results for evaluating the visual acuity recovering time.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed our in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, a visual acuity testing apparatus comprises a casing having at least one test windows which an examinee looks into and at least one optotype presented inside the casing which is disposed in such a position that its optotype plane is tilted relative to a datum plane orthogonal to an axial line connecting the test window to an optotype presentation position in order to prevent that light entered through the test window and reflected from the optotype plane, passes through the test window again. In another aspect of the present invention, a visual acuity testing apparatus comprises two casings for a right eye and for a left eye having a test window and an optotype presentation window respectively and also having approximately equal distances from the center axis of the test windows to a right wall and to a left wall respectively, optotypes including the same set of optotypes which can be disposed in each of optotype presentation windows simultaneously, inside illuminating means which illuminates the inside of each of the two casings respectively, optotype illuminating means which illuminates each of optotypes disposed in each of optotype presentation windows respectively, test eye designating means which for designating an eye to be examined among a single right eye, a single left eye, and the both, and illumination controlling means which controls the inside illuminating means and the optotype illuminating means separately based on designation by of the test eye designating means. Further, in another aspect of the present invention, a visual acuity testing apparatus comprises mode instructing means which for giving instructions a night visual acuity test for measuring visual acuity recovering time, optotype presentation means which presents at least one test optotype, response means for making a response of a judgement result on the presented optotype, measuring means which measures lapsed time from start of presenting optotype to the response in order to measure the visual acuity recovering time based on the instructions given by the mode instructing means, judging means which judges whether the response agrees with the presented optotype, and determining means which determines a test result based on the number of consecutive right responses or the number of consecutive wrong responses. Furthermore, in another aspect of the present invention, a visual acuity testing apparatus comprises mode instructing means for giving instructions to perform a night visual acuity test for measuring visual acuity recovering time, measuring means which measures lapsed time from start of presenting optotype in order to measure the visual acuity recovering time based on the instructions given by the mode instructing means, optotype presentation means which presents at least one optotype, optotype illuminating means which illuminates the presented optotype, response means for making a response of a judgement result on the presented optotype, and illumination controlling means which changes the amount of illumination light volume by controlling the optotype illuminating means based on presence or absence of the response and the lapse time measured by the measuring means.